An aircraft turbojet is generally positioned in an external shell called a “nacelle”. A partial schematic longitudinal section view of a conventional arrangement of a fan with removable blades in a nacelle is illustrated in FIG. 1. The nacelle of the turbojet contains an air inlet upstream section 110, which is extended downstream by a section 120 including a casing 121 called the fan casing, intended to surround a fan of the turbojet. The fan includes a blade assembly which contains a plurality of blades 140.
The role of air inlet section 110 is to capture the air intended to feed the turbojet, whilst ensuring optimum air flow as far as an inlet plane of the fan. In particular, the air must be decelerated as far as the fan's inlet plane. For example, during cruising, the Mach number thus changes from 0.8 in outside conditions to 0.6 in the area of the fan's inlet plane. To accomplish this, air inlet section 110 has a curving internal wall 111 extending longitudinally as far as fan casing 121.
The turbojet's fan includes a rotary disk 130, the periphery of which contains a plurality of recesses 131. Each blade 140 of the fan includes an attachment 141 housed in one of recesses 131 of disk 130. Attachment 141 of a conventional blade 140 is generally rectilinear, but there are also blades with a curvilinear attachment which have a curvature in a plane tangential to the periphery of disk 130.
Document FR 2903154 A1 describes an example of an installation of a fan blade where each blade has a curvilinear attachment with a curvature in a plane tangential to the periphery of the disk.
To remove a blade 140 of the fan in the conventional manner, a cone 150 located upstream from disk 130 of the fan is removed beforehand, as illustrated in FIG. 1. A shim positioned in recess 131 of disk 130, between attachment 141 of blade 140 and the base of recess 131, is then removed. Blade 140 is then moved radially by a certain height permitted by removing the shim, and blade 140 is then disengaged from recess 131 by sliding attachment 141 longitudinally in recess 131. In this manner, blade 140 is removed by passing through air inlet section 110 without coming into contact with it.
However, the current trend is towards an increase of the rate of dilution of turbofans, also called the BPR (By-Pass Ratio). The rate of dilution is equal to the ratio between the flow rate of the secondary stream and the flow rate of the primary stream of the air in the turbojet. To increase the rate of dilution the diameter of the nacelle is increased, which has disadvantages, such as increased nacelle mass and drag.
The design of the nacelle is then revised to reduce the impact of these disadvantages. With this aim, the length of the air inlet section is reduced. The term “short” air inlet section is then used. A partial schematic longitudinal section view of an example of a nacelle containing a short air inlet section is illustrated in FIG. 2.
Despite a shorter length, air inlet section 110 must keep the same capacity to provide an optimum air flow as far as the fan's inlet plane. To accomplish, inner wall 111 of air inlet section 110 penetrates further under casing 121 surrounding the fan.
In this configuration, inner wall 111 prevents a blade 140 of the fan from being removed. Indeed, the space is insufficient to remove completely attachment 141 of blade 140 from recess 131 of disk 130, since blade 140 comes into contact with inner wall 111 before it can be removed completely.
It is then necessary to remove air inlet section 110 of the nacelle in order that blade 140 is able to be disengaged longitudinally. However, this solution has the disadvantage that it is extremely time-consuming due to the presence of many devices in air inlet section 110 of the nacelle, for example de-icing systems.